In soils with very high 2:1 clay contents, the soils expand and contract as they are wetted and dried. This creates shear faces called slickenslides, like the one shown above. Essentially they clay expands so much it's forced to shear somehow, and this is the resulting shear plane.
More like a piece of chicken breast that you cooked a bit too long, which fell on the floor, which you then kicked under the fridge, and which then slid out the door and rolled around in the dirt a bit.